Electrics, KVA, can someone explain this please?

macafee2 · 10th April 2021, 18:14

Power requirement : The normal maximum capacity for individual
domestic properties is 15kVA.

At 230v for a domestic house, how many amps is 15kva? Trying to find out how many amps I can draw before melting the incoming power supply cable.
For now lets pretend there is nothing to protect the incoming supply.
The network operator wont tell me how much current I can draw because I may try to draw that amount of current. yea, so? If you tell me that is what I can draw, and that is what I draw, whats the problem?

Even working out what one may draw is not as easy as one may think.
fridge, freezer, cooker, washing machine, tumble dryer, toaster, kettle, electric heaters bla bla bla.
My compressor will momentarily at start up draw 30 amps but drop back to 20 when running. Ask a number of manufacturers the start up value of their products and you blow their minds.

macafee2

another_clean_sheet · 10th April 2021, 18:21

65.2 amps @230volts

COLVERT · 10th April 2021, 19:51

The safety level on the incoming cable is very high. You would have to draw a lot of power to melt that.---

15K is 15,000.---Divide that by 230 to find the available amps.

As the previous post says 62.5 amps.---

macafee2 · 10th April 2021, 22:15

Quote:

Originally Posted by COLVERT

The safety level on the incoming cable is very high. You would have to draw a lot of power to melt that.---

15K is 15,000.---Divide that by 230 to find the available amps.

As the previous post says 62.5 amps.---

ok i get 15k is 15,000. If you have the watts, I get the divide by 230 to get the amps, what i did not get was the va. Normally I would presume v is volts and a is amps but va together, that is what lost me. What is a kilovolt amp? I have not heard the term before.

62.5 amps, that seems low for a house. When I think of what the washing machine, kettle, dishwasher, tumble drier all take. I must be missing something.

macafee2

Roverlike · 11th April 2021, 06:06

Watts and Volt Ampers both show the power appliance is using. Formula for power is U= I x V. Since I is current measured in Ampers and V is voltage measures in Volts, term VoltAmps is used.

Difference is in fact that in case of DC power you can use Watts without problems.

However when you are talking about AC power you need to be careful. Do you realy get 230 Volts from power lines into your house? I do not think so. That is the reason why it is always said that voltage is 220V-230V . Point is that VoltAmps represent actual power used from your appliance. If you have number of ampers from your appliance and multiply by 220V you will get one power and if you multiply by 230 you will get another power. That is the reason why it is said VoltAmps - this is actually warning to take care of what and how you are using it.

Also, if you are making any calculations of AC power, you need to have reserve in these calculations, meaning you might take more power if power lines distribute more than 230V. This also could happen, and in that case you need to be sure something is not burnt.

macafee2 · 11th April 2021, 07:04

perhaps i should just look at the main fuse, what ever that is rated at I should be able to draw, I just cant get to it for now.

62 amps seems very low, if that is the standard supply why is the main fuse a 100?

macafee2

Roverlike · 11th April 2021, 07:42

Among other things, reserve serves on motor starting as more current is drawn from the power network. However, you should have stated what current is drawn at startup on appliance and calculate your power even slightly above that (remember difference in Volts 220-230V).

Fuses are created in standard forms, so you will not have fuse for 62 amps. However you can ask why it is not 80 amps then but 100 amps fuse. When standardisation is done they needed to include power consumed at that time and forseen power that might be taken in next decades. It is not useful to build something which will need to be replaced completly when consumer power rises. It would cost a lot.

Having fuse of 100 amps actualy protects the power network from you this is standard they set up and build network up to that standard. And they will not let you use more power than that.

I can go further in my explanation and set terms like active/useful and reactive/unuseful power. These two powers exist in case current and voltage are not in same phase in case of AC power. Power network needs to be built to sustain both of these powers and that reactive lower actualy represents the reserve you have in case of AC power. But I will not go further and possible start confusing readers.

SD1too · 11th April 2021, 08:03

Quote:

Originally Posted by Roverlike

Since I is current measured in Amperes and V is voltage measures in Volts, term VoltAmps is used ... If you have number of amperes from your appliance and multiply by 220V you will get one power and if you multiply by 230 you will get another power. That is the reason why it is said VoltAmps ...

Eh? I'm sorry, that is not an explanation! Watts results from the same formula in both cases so the question remains, why not use that?

This, from UK Power Networks, also brushes over any credible reason:
https://www.ukpowernetworks.co.uk/he...-kilovolt-amps

In recent years there's been a certain amount of the reinvention of the wheel. Some people have decided that terms which have been in common use for decades, if not centuries, need to be abandoned and replaced with something different which essentially has the same meaning. For example, in the electrical world, "surge" has been replaced by "inrush".

It's completely unnecessary! I think that the reason is ego. Mysterious technical terms are bandied about freely by people who want to appear important and intellectually superior to everybody else. I suspect that is what's behind "volt-amps" but I will ask a friend of mine who has worked in the electrical design field all his life. It may be that my cynical view is completely wrong!

Simon

another_clean_sheet · 11th April 2021, 10:03

Quote:

Originally Posted by macafee2

This reserve, is this the start up amperage, when a motor starts it draws more current then when it is running?

macafee2

It depends if the main fuse is anti surge fuse or not

COLVERT · 11th April 2021, 12:24

Quote:

Originally Posted by macafee2

This reserve, is this the start up amperage, when a motor starts it draws more current then when it is running?

macafee2

The surge happens at start up because for a split second the motor acts as a dead short until it starts to spin up.----

10th April 2021, 18:14	#1
macafee2 This is my second home Rover 75 Saloon & Tourer Join Date: Sep 2012 Location: Lincoln Posts: 14,928 Thanks: 1,630 Thanked 3,032 Times in 2,181 Posts	Electrics, KVA, can someone explain this please? Power requirement : The normal maximum capacity for individual domestic properties is 15kVA. At 230v for a domestic house, how many amps is 15kva? Trying to find out how many amps I can draw before melting the incoming power supply cable. For now lets pretend there is nothing to protect the incoming supply. The network operator wont tell me how much current I can draw because I may try to draw that amount of current. yea, so? If you tell me that is what I can draw, and that is what I draw, whats the problem? Even working out what one may draw is not as easy as one may think. fridge, freezer, cooker, washing machine, tumble dryer, toaster, kettle, electric heaters bla bla bla. My compressor will momentarily at start up draw 30 amps but drop back to 20 when running. Ask a number of manufacturers the start up value of their products and you blow their minds. macafee2

11th April 2021, 07:42	#7
Roverlike Avid contributor Rover, few of them Join Date: Aug 2011 Location: Split, Croatia Posts: 235 Thanks: 254 Thanked 117 Times in 82 Posts	Among other things, reserve serves on motor starting as more current is drawn from the power network. However, you should have stated what current is drawn at startup on appliance and calculate your power even slightly above that (remember difference in Volts 220-230V). Fuses are created in standard forms, so you will not have fuse for 62 amps. However you can ask why it is not 80 amps then but 100 amps fuse. When standardisation is done they needed to include power consumed at that time and forseen power that might be taken in next decades. It is not useful to build something which will need to be replaced completly when consumer power rises. It would cost a lot. Having fuse of 100 amps actualy protects the power network from you this is standard they set up and build network up to that standard. And they will not let you use more power than that. I can go further in my explanation and set terms like active/useful and reactive/unuseful power. These two powers exist in case current and voltage are not in same phase in case of AC power. Power network needs to be built to sustain both of these powers and that reactive lower actualy represents the reserve you have in case of AC power. But I will not go further and possible start confusing readers. Last edited by Roverlike; 11th April 2021 at 07:50..

10th April 2021, 18:21	#2
another_clean_sheet Posted a thing or two Rover 75 CDTI Tourer Join Date: Nov 2014 Location: Great Bardfield, nr Braintree Posts: 1,414 Thanks: 303 Thanked 436 Times in 317 Posts	65.2 amps @230volts

10th April 2021, 19:51	#3
COLVERT This is my second home R75 Saloon. Join Date: Feb 2009 Location: France/or Devon. Posts: 14,003 Thanks: 3,851 Thanked 2,167 Times in 1,816 Posts	The safety level on the incoming cable is very high. You would have to draw a lot of power to melt that.--- 15K is 15,000.---Divide that by 230 to find the available amps. As the previous post says 62.5 amps.---

11th April 2021, 06:06	#5
Roverlike Avid contributor Rover, few of them Join Date: Aug 2011 Location: Split, Croatia Posts: 235 Thanks: 254 Thanked 117 Times in 82 Posts	Watts and Volt Ampers both show the power appliance is using. Formula for power is U= I x V. Since I is current measured in Ampers and V is voltage measures in Volts, term VoltAmps is used. Difference is in fact that in case of DC power you can use Watts without problems. However when you are talking about AC power you need to be careful. Do you realy get 230 Volts from power lines into your house? I do not think so. That is the reason why it is always said that voltage is 220V-230V . Point is that VoltAmps represent actual power used from your appliance. If you have number of ampers from your appliance and multiply by 220V you will get one power and if you multiply by 230 you will get another power. That is the reason why it is said VoltAmps - this is actually warning to take care of what and how you are using it. Also, if you are making any calculations of AC power, you need to have reserve in these calculations, meaning you might take more power if power lines distribute more than 230V. This also could happen, and in that case you need to be sure something is not burnt.

11th April 2021, 07:04	#6
macafee2 This is my second home Rover 75 Saloon & Tourer Join Date: Sep 2012 Location: Lincoln Posts: 14,928 Thanks: 1,630 Thanked 3,032 Times in 2,181 Posts	perhaps i should just look at the main fuse, what ever that is rated at I should be able to draw, I just cant get to it for now. 62 amps seems very low, if that is the standard supply why is the main fuse a 100? macafee2